Isochronous governor



Dec.'25,l 1962 M. R. ADAMS ETAL 3,070,073

IsoCHRoNoUs GOVERNOR Filed Dec. 29, 1960 2 Sheets-Sheet 1 ram/LJ 32 4 Pf 62 56 [DI 6 -54 y mt 6m( :(30

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The present invention is directed to governor apparatus and more particularly to' governor apparatus for controllingthe governed operating speed of an engine and which is readily adjustable, preferably externally, to provide either proportional or isochronous governing operation.

lroportional or droop type governors and isochronous type governors each have separate characteristics which makes one type more suitable as a control in one situation than another. For example, proportional governors generally have rapid response and good stability, however, they permit a speed shift of a certain amount with variations in engine load. Isochronous governors on the other hand maintain nearly a constant engine speed for all load variations, but are generally inferior in response rate and stability as evidenced by hunting, overshooting, or excessive time required to stabilize. It is desirable therefore to match the type of governor operation to select the most suitable for a given load. Further, it is often desirable to alternate the type of governor operation for a given load. For example, in electrical power generation systems having multiple power plants connected to a common load it is desirable to have one isochronous control unit to allow for load iiuctuations. it is further desirable to alternate from time to time the unit being driven isochronously since it is subject to greatest wear.

Consequently, it is an object of the present invention to provide a governor apparatus which may be readily adjusted without dismounting or disassembling the control unit to provide either proportional or isochronous operation.

It is a further object of the present invention to provide governor apparatus having improved isochronous operation by the provision of a separate integrating piston in combination with a proportional type governor which permits the more stable proportional system to correct the major portion of any speed error whereas the integrating piston is required to correct only small errors.

is a still further object of the present invention to provide a governor having separate proportional and integrating parts, but requiring only a single speed sensor to actuate both sections.

Other objects and advantages of the present invention will become apparent on consideration of the description read in conjunction with the appended drawings wherein:

i is a schematic drawing of a system wherein our governor may be used;

FlGUll 2 is a more detailed schematic of a preferred embodiment of our governor including the novel aspects of our invention;

3 is a first curve showing some of the operating characteristics of our invention as brought out in a plot of speed vs. fuel flow in the system of PlGUll l; and

FlGUllE 4 is a second curve illustrating some operating characteristics that may be brought out in a plot of speed vs. time.

Referring to FlGURE l there is illustrated a system which our governor may be used and is roadly com- .rised of power plant ltl and fuel supply system l2. Power plant lli is illustrated as a gas turbine engine having an air inlet llE, an air compressor unit Ltd, a turbine lo, and a drive shaft id enabling the turbine to drive the compressor. A series of can type combustion chambers are annularly arranged about the interior of the engine intermediate the compressor and turbine and receives fuel from manifold 22 through `individual fuel nozzles 24%. Gas turbine lil also includes an exhaust or tail' e section Zd.

Fuel supply section l2 has as its broad object the task of supplying a metered quantity of pressurized fuel to lthe manifold 22 and to thereby control the operating characteristics of the engine. To achieve this object fuel maintained in tanlt 2S is delivered at a relatively low pressure, designated P0, to inlet conduit 3u which contains positive displacement gear pump 32 which may be driven by any convenient source, such as for example the engine lil. Pump 32 operates to raise the fuel pressure to a relatively high value, designated P1, and discharge fuel into pump outlet conduit 3d. Fuel in conduit is transmitted past a by-pass valve generally indicated at 36 to meteriniy valve 33 which is slidably positionab-le in a manner to be described to control the quantity or rate of fuel delivered to metered fuel conduit Fuel in conduit is at a lesser value than F1 due to the throttle eiect of valve 3S and is designated P2 pressure fuel. Conduit do is connected to engine manifold E2 to supply the metered fuel thereto. By-pass valve 36 is provided to control the pressure difference across metering valve (Plhl), to a constant value such that the quantity of metered fuel to conduit lll will be solely dependent on the position of said metering valve and not on fluctuations or variations in supply pressure. To achieve this end a valve member is provided to con- -trol the flow of fuel from conduit 34E to conduit lid, said conduit ld being connected to conduit 3d and thus coutaining relatively low pressure P0 fuel. Thus depending on the position of valve member d2, varying quantities of fuel are returned to the pump inlet for recirculation. Valve member 42 is secured to a diaphragm which is exposed to 'P1 pressure fuel on the lower side from conduit 34 and P2 pressure fuel on the upper side from conduit Il@ by means of conduit which includes a restrictive damping bleed 5d, such that diaphragm is responsive to and will control the operation of valve member as a function of the difference in pressure be weon P1 and P2 fuel. Spring 52 is provided to provide a preload to diaphragm so which determines the magnitude of the difference between lil-P2 pressures.

Thus the rate of flow of metered fuel is determined solely by the axial position of metering valve: 3d which in turn is positioned by positioning means comprised of the two diaphragms 5d and 56, the rod 58 connecting said diaphragms and pivoted lever du which is secured to rod 5S on one end and metering valve 38 on the other, such that any movement imparted to diaphragms 54 and Se is transmitted to metering valve 38. P1 pressure fuel from conduit 3d is exposed to the inner surfaces of diaphragms 5d and 56 to provide equal and oppositely aoting pressure induced forces `acting on rod S3 which balance or neutralize each other. A reference force generally proportional to the movement of the diaphragm and rod assembly is applied to the upper surface of diaphragm 5d by spring d?. and also the minor force produced by relatively low pressure io fuel supplied by conduit :63 from pump inlet conduit Btl. rI'his force is generally proportional to diaphragm movement since as diaphragm 5d is moved up or down it will compress or elongate spring 62 thus varying the force said spring produces. A servo control iiuid designated PX is supplied to the lower surface of diaphragm 5d by way of the circuit dened by conduit 64, which includes constant pressure regulating valve 66, conduit 63 which includes restrictive servo bleed 79, and branch conduit 72. Fuel pressure aarden/a at the discharge side of valve do would be maintained at a relatively high constant pressure in the preferred form of our invention designated at PR, but it is pointed out that the purpose for doing so is to maintain a substantially constant pressure difference between PR and P0 fuel which may alternately be done by permitting PR to vary as long as it did so substantially uniformly with P0. Ey bleeding off fuel in conduit 63 downstream of restriction 7d the PX pressure therein may be varied to any convenient value between the limits of the source pressure PR and the dump or reservoir pressure P0 and thus vary the fluid pressure force acting on the lower surface of diaphragm 56 and thus the position of metering valve 3S and the rate of flow delivered to manifold 22.

To further complete the showing of a fuel supply system we have illustrated in FlGURE 1 two basic control systems comprised of unit 74 and a governor control unit 76 which may contain means for bleeding off fuel from conduit 7.2 through ltheir respective connecting conduits '78 and 8d. Since the aspects of the present invention are fully contained within the governing unit 76 it is pointed out that the details of the acceleration and deceleration unit 7d may be in accordance with any such unit well known the art having the broad purpose of limiting or controlling fuel during engine acceleration and/or deceleration ranges of operation. rl`he broad teaching of a suitable arrangement and selection of engine parameters for effecting this object may be found in US. Patent 2,581,275 issued to Frank C. Mock and having a common assignee with the present application.

This system described to this point is for the purpose of illustrating a fuel supply system that may be readily controlled to meter fuel to an engine by the simple expedient of bleeding off more or less fluid from a conduit such as conduits 63 and/ or 72. llt is -to be understood that the description is intended to disclose a general class of fuel systems and the specific relation of the parts may be readily varied to suit particular requirements.

Governor unit 76 operates to bleed off more or less fuel from conduit 68 through branch conduit 80 in response to an engine speed input signal derived from mechanical connection 82 and the position of the throttle lever Sd. PR pressure fuel is supplied as an operating control fluid to governor 7d by Way of conduit 64 and low pressure fuel is returned to pump inlet by the connecting conduit 86. External screw head adjustments 38, 9d yand 92 are provided for purposes which will later be described in detail.

Turning now to FXGURE 2 there is shown a cross sectional schematic vicw of our governor illustrating in detail a preferred embodiment of our invention. Portions of the fuel supply system carried over from FIGURE l bear the same reference numerals assigned therein. Governor 76 is comprised of a housing 94 defining a first chamber 9d and a second chamber 93. A pair of flyball governor weights 1li@ are arranged in chamber @d and are pivotably secured at 192 to bracket 1M which in turn is secured to rotating connection d?, which is driven in relation to engine speed. The force produced due to centrifugal forces acting on the rotating weights 18d tends -to urge the weights outwardly from their spin axis so that the extended foot proiections 1% thereof are urged upwardly and bear against the enlarged portion lieti of the rod 11d with a force proportional yto engine Speed. Rod 11@ is secured to lever 112, which is pivoted at 114 and is comprised of a first leg 11d and a second leg 113 shown in the illustrated embodiment as at substantially right angles to one another. The angular relation of legs 11d and 11S is, however, non-essential to practice the invention. generated by flyweights llfifl is produced by spring 12@ which is confined between retainers 122 and 124, the latter being pivotally secured to housing M at 1%. This 'second force is transmitted downwardly through roller 123, which may be translated by means of external ad- A second force acting to oppose the force l justment 92, to lever 112 and thus oppose the force generated by the flyweights. An externally extending throttle member 34, pivoted at 13d, engages retainer 122 so that the force bearing down on lever 112 is in direct response to lthrottle position. lt will aid in understanding the present device to consider that the force produced by spring 126 is representative of desired or selected speed that the operator wishes the engine to run whereas the force produced by fryweights lili) is representative of actual engine speed7 such that when the two forces are in balance the engine is running at substantially the selected speed, and when the forces are not in balance a certain departure exists between selected speed and actual speed which may be termed speed error. The speed error force acting on lever i12 will tend to rota-te said lever about pivot .ws-g clockwise when the actual speed force is less the desired speed force, and counterclockwise when the tal speed force is greater than the desired speed force. The second leg 11S of lever 112 includes first and second valve portions 132 and 13d respectively which may be either independent valve members or formed as part of lever 112 as illustrated in FlGURE 2. Movement of said first and second servo valve members is in direct relation to the movement of lever 112. A movable servo orifice member 136 is slidably mounted in housing 94E- and is arranged in close proximity to valve portion 132 such that the relative position of said orifice member with respect to said valve defines the effective fluid dow permitting area and thus ythe rate at which fluid is bled through conduit Si? from conduit 68 downstream of restriction 7i?. As servo orifice member 136 `and valve 132 move relatively further apart, the effective area is increased bleeding more huid from conduit eS and thus lowering the pressure acting on diaphragm 56 and thus regulating engine fuel delivery. A hydraulic pision member of the diiferential area type is generally designated by numeral 13S iand is slidably disposed in the second chamber 9S formed in housing 94. Piston 13S is comprised of a largefdiameter land le@ and a smaller diameter land 142 connected by rod 144 and are arranged to denne three compartments 146, 15a-3 and 150 within chamber 98 and in cooperation with housing 94. It is the purpose of a hydraulic piston member 138 to control the position of movable servo orifice member 13d to which it is connected by a first link 147 pinned to piston 13S at 149 and a second L-shaped link 151 pivotably secured yto housing 94 by pivot 153 and pinned to first link 147 at 155. A foot portion 157 of second link 151 is inserted between bracket 159 formed on movable servo orice 136 so that angular movement of link 151 will move orifice member 13d axially in response to movement of piston 133. Relatively low pressure P0 fluid via return conduit Se and chamber 96 is permitted to flow into compartment fell wherein it provides a relatively small force acting upwardly on land 142 tending to move piston 133 upwardly. Relatively high regulated pressure, PR, is supplied by conduit 64 to compartment .1e-8 intermediate lands 146) and 142 providing a net force [PRX(A140A142)] where A is the area of the respective lands designated by subscript acting upwardly on piston 13S. Since in the preferred embodiment of our invention P0 is relatively small and PR substantially constant, the net force described to this point iactinfJ to position piston 13S upwardly is substantially constant and #.1 will remain so regardless of movement of piston 13S within chamber 98. A conduit 152, including a restriction 1515i, is provided to supply control fluid from compartment ldd to compartment 1de. Restriction 154 operates to limit the quantity of fluid supplied to compartment 146 such that by varying the quantity of fuel bled from conduit 152 downstream of restriction 15d the pressure in compartment 14d may be varied to any desired value within the limits of PR to P0 and is designate PZ pressure uid. Conduit 156 is connected to conduit im downstream of restriction 154 on one end and to a non,

fixed servo orice member 158 on the other. Servo orifice 158 is arranged in close proximity to servo valve member 134 so that said orifice and valve members define a variable effective flow permitting area capable 0f bleeding off varying quantities of fluid from conduit 156 and thereby vary the value of PZ pressure. An adjustable restriction is provided in conduit 152 downstream of the connection of conduits 152 and 156 operates to limit the rate iiuid can liow into compartment 146. PZ fluid pressure in compartment 146 acts downwardly on land 14d to provide ia force tending to move piston 138 downwardly in opposition to the previously described substantially constant net force tending -to move the piston upwardly. PZ iiuid will have a pressure value therefor that will exactly balance out the upward forces which may be termed its null value. Any value of PZ pressure greater than null will cause said piston to move downwardly, any value less than null will permit the piston to move upwardly. The greater the deviation of PZ from its null value, the greater will be the force unbalance thereacross and therefore the faster piston 138 will move. Thus the velocity of movement is dependent on the degree of departure of PZ pressure from its null value. Adjustable bleed 85 by limiting the rate fluid can flow into or out of compartment 146 and therefore the rapidity that PZ pressure can be changed will operate as a velocity adjustment for piston 138. A second adjustable bleed 90 is provided in conduit 152 upstream of the connection between conduits 152 and 156 which is adjustable to provide either proportional or isochronous operation in a manner now described. When adjustable restriction 9@ is wide open it has no effect on the system; when closed restriction 9d stops iiuid flow through restriction 15d permitting PZ to equal P0 pressure supplied by conduit 156. As a result piston 138 will move to its extreme upward position and remain there regardless of movement of valve 13d as long as adjustable restriction 9d remains closed.

FIGURE 3 shows some of the operating characteristics of our invention as illustrated by a plot of fuel flow (Wf) vs. speed (N). Curves 15d and 162 represent maximum and minimum fuel flow limits for acceleration and deceleration of the engine respectively as determined by the acceleration and deceleration control 74 of FIGURE l. Curves 164, 166, 158 and 17? represent various governing curves to illustrate the operation of our invention. Curve 3.72 represents a steady state or equilibrium condition of operation where for a given engine load and ambient air conditions the curve represents the fuel required to maintain a stable speed, that is neither accelerating or decelerating. Curve 174 represents a second steady state curve which would be occasioned by a change in engine load or ambient air conditions. For consideration of the operation of our device the following conditions can be assumed -to prevail: engine load and ambient air conditions are such that the steady state curve is the curve 172; the engine is running iat a stable or equilibrium speed; governor settings are approximately as illustrated in FIGURE 2 with the exception of adjustable bleed 91B which is screwed into its oit position whereby piston 133 maintains a constant position at the extreme upward location of its travel range. Under the assumed conditions of operation governor operating characteristics are represented by curve 16S and the fuel flow rate and engine speed is represented by the ordinate and abscissa respectively of point A defined by the intersection of curves 155 and 172. Further, under the assumed conditions of operation, the force moment acting on lever 112 due to flyweights 199 is balanced by the force moment produced by spring 120 so that lever 112 has a constant position and maintains iX pressure in conduit ed and acting on diaphragm 56 at a value necessary to maintain the required fuel dow. if engine load is then increased or ambient `air conditions change so that curve 174 represents a new steady state condition, the engine speed and flyweig'nts 11i@ will begin to slow down since the fuel being supplied at point A is less ythan that required to maintain stable speed on curve 74. As the force from flyweiglits 161i acting on lever i12 drops, lever 112 will move clockwise bringing valve closer to servo orifice member 136 and thus increase PX and also engine fuel tiow. Speed will continue to drop and fuel flow to iiicrease until the system stabilizes at the new equilibrium point B defined by the intersection of curves 163 and 174. lit will be noted that throughout the range dened by curve 158 a speed shift is necessary to produce a fuel flow change. This relationship may be termed the proportionality or gain of the droop or proportional type governor represented by slope of curve 168. Generally the greater the proportionality the more stable will be control and engine operation, however, where precise regulation of speed is required such a system is decient.

Gne of the features of our device is the provision of an easy, preferably external adjustment for varying the slope of the governor curve and thus control the degree of proportionality. By means of external adjustment 92, roller 123 may be positioned a certain degree to the right or left of the position illustrated in FIGURE 2 and thus increase or decrease the slope of the governing curve. By way of example, if rolier 1.,@ is adjusted to the richt a certain distance from the illustrated position the moment arm of the force produced by spring 12@ is increased. After such an adjustment the governor curve will be in accordance with curve idd wher-ein the greater moment arm for the force from spring 12d will decrease the steepness of the governor curve. it is evident that a change from steady state curve 17?. to will cause a larger speed shift on governor curve los as represented by the listance between points A and C along the abscissa of FIGURE 3 than on curve 163 between the points A and B. Thus the degree of proportionality or slope of the governing curve may be adjusted by movement of roller 12S.

If now adjustable bleed 9d is opened to permit movement of piston 133, governing operation will occur in accordance with curve 154.'- such that a change is steady state will not cause any speed shift and operation of the governor is termed isochronous Assume the steady state is curve 172 and equ'librium exist at the paint A. The opeosing forces of weights 16d and spring 1Z0 are again balanced, PX is sufficient to maintain the required fuel flow represented by the ordinate of point A and PZ pressure is at its null value with piston 13S stationary. If steady state were then changed to curve 174i speed would drop since the fuel fow at point A is less than that required to maintain stable speed at the new equilibrium point D defined by the intersections of curves 164 and 171i. As a result of a momentary speed decrease and a reduction in the force output of weights ili, lever 112 rotates clockwise initiating two simultaneous actions. First, servo valve 132 wiil move cioser to orifice member T135 raising PX pressure and increasing fuel in the manner previously described for example between points A and B. Secondly, servo valve 13d will advance closer to orifice 15in increasing PZ pressure above its null value so that piston 13S begins to move downwardly. Downward movement of piston transmitted through mechanical connection 151 will position movable servo orifice member 135 further to the right, thus further reducing the eiiective flow permitting area defined by orifice 136 and valve 132 and further increasing PX pressure. Piston 138 will continue to move until PZ pressure again attains its null value which occurs at only one position of valve 134, thus lever 112 will return to its original position so that the point D has the saine speed or abscissa as point A.

When it is desired to operate an engine at different speed from that indicated by the abscissa of points A or D, throttle lever @d may be reset to provide a different force from spring 12u. For example, to select a lower aernovs speed throttle is moved clockwise allowing spring i2@ to elongate and reduce the force on lever 112. Lever ill?, will move counterclockwise reducing PX and PZ pressures which results in a decrease in engine fuel and a consequent decrease in engine speed. Speed will decrease until the force produced by llyweights i? drops to tbe point where it balances the new lower spring force as for example at the point E on curve ltl of FlG- r1he new regulated speed will then become that engine ure s. represented by the abscissa of point E.

FlGURE 4 is a graph showing further operating characteristics of our device as illustrated by a plot of engine speed (N) vs. time (T). Curve 17S represents this relationship for proportional operation as when adjustable bleed Si@ is closed. if at the time T1 the engine experiences a sudden increase in load, the control unit will provide a corrective increase in fuel during the elapse time Tl--TZ and will restablize at time T2. However, due to the previously mentioned speed shift, stabilization will occur at a slightly lower speed represented by the departure of curve ll from the dash line at times greater than T2, Curve ld represents the speed vs. time relationship for isochronous action when adiustable bleed 90 is in the open position. It will be observed that a greater time is needed for stabilization, 'f1-T3, however, no speed shift will be experienced. The elapse time for stabilization may be varied by adjusting velocity control bleed 33. For example if bleed 8S is adjusted in a further open position so as not to restrict the iiow of liuid between compartment Ellie andl passage l5?, the speed vs. time relatonship may be as illustrated by durve lltZ where stabilzation occurs in the time 'f1-T4.

lt should be understood that the adjustments and movements of the governor parts described above are of a reversible nature and movements in direction opposite to those described will induce similar functional changes in opposing directions. Further, the description is of a preferred embodiment of our device and it is contem- Llate that changes within the skill of the ordinary mechanic skilled in the art may be made without departing the scope of the present invention.

We claim:

l. In a governor for controlling an engine fuel supply 'the combination of a movable iuid pressure responsive voutput member for controlling fuel delivery, conduit means for supplying a pressurized control fluid to said output mcrnbe, a movable servo orifice member connected to said conduit means for varying the fluid pressure therein in response to the effective servo orifice area, a pivoted lever member having a first servo valve formed thereon, said first servo vaive member being operative with said movable servo orifice to control the effective thereof in response to movement of said pivoted lever me riber, a centrifugal tl'ywbeight adapted to be driven in relation to engine speed connected to said pivoted lever member to apply a speed generated force thereto tending to rotate said pivoted lever member in a first direction about its pivot, a throttle member, a spring contained between said throttle member and said pivoted lever member to apply a second force tending to rotate said lever member in a second direction about its pivot in proportie to throttle position, a dierential area piston member connected to said movable servo orifice member to move said movable servo orifice member with respect to said o valve member and thereby vary the effective thereof in response to movement of said diilierei'itial area piston, said conduit means operative to s nply pressurized control fluid to said dierential area "l, said conduit including a restriction therein an ged so that control fluid is supplied in limited quanti es to one side of said differential area piston, a fixed servo orice, passage means iluidly interconnecting said servo orifice and the limited quantity of said conti fluid acting on said one side of said differential area piston, and a second servo valve member formed on said U pivote lever and operative with said fixed Servo orifice to control the effective area thereof in response to movement of said pivoted lever.

2. ln a governor system for controlling fuel delivery to an engine, the combination of fuel con-trol means for controlling the rate of fuel supplied to the engine in proportion to a variable uid pressure, a pressurized control fluid source, first conduit means including a fixed restriction therein interconnecting said fuel control means and pressurized control fluid source, a first servo orifice member fluidly connected to said first conduit means downstream of said restriction, governor means adapted to produce a force indicative of engine speed error, a pivoted lever connected `to said governor means and movable in response to said speed error force, said pivoted lever further operative with said first servo orice member to control the effective area thereof, a hydrauli pistonv member connected to said first servo orice member to cont-rol the position or" said first servo valve member and ther-eey further control the effective area thereof, second conduit means interconnecting said hydraulic piston and said pressurized control ilu-id source operative to suppiy a limited quantity of duid to one side of said piston and an unlimited quantity of lluid to another side of said piston, .a second servo orifice member having a fixed position, .and a passage connecting said second servo orifice with the limited quantity of fluid on said one side of said piston member, said pivoted lever being operative with said second servo orifice member to control the effective area thereof.

3. ln a governor system for controlling fuel delivery to an engine, the combination of pressure responsive means operative to control the fuel delivery rate in proportion to a variable uid pressure input, first and second movable servo control members jointly operative to define a rst effective area which is variable in response to relative movement of said first and second servo control members, control iiuid supply means operative with said pressure responsive means and said first effective area to provide said iuid pressure input that is varied in direct relation to said rst effective area, a pivoted lever connected to one of said first and second servo control members to control the position thereof and thereby vary said first efiective area, a centrifugal flyweight member adapted to be driven in relation to engine speed connected to said lever to apply a first positioning force thereto, a throttle lever, a spring member connected to said throttle lever and said pivoted lever to apply a second posi-tioning force to said lever in opposition to said first force and which is 'variable with throttle position, a piston member connected to the other of said first and second movable servo control members to vary said first effective larea in response Vto movement thereof, means supplying a restricted quantity of pressurized control 'liuid to said piston member, a third fixed and a fourth movable servo control member jointly operative to define a second effective area which is variable in response to movement of said fourth movable servo control member, and passage means interconnecting said restricted quantity of control fluid acting on said piston and said second effective area, said fourth movable servo control member being connected to said pivoted lever for movement therewith.

4. ln a governor, the combination of hydraulic servo means includ ig a first movable servo valve yand a movable servo ormce member jointly operative to control a fluid output pressure, governor liyweight and spring means connected to said first movable servo valve to control the position thereof and thereby vary said fluid output pressure, a ydifferential area piston connected to said movable servo orifice member to control the position thereof and thereby vary said fluid output pressure, a regulated pressure control iiuid source, tiret passage means transmitting regulated pressure control duid from said source to one side of said differential area piston, second passage means including a restriction therein transmitting control duid from said source to another side ot said piston, a fixed servo orifice, third passage means fluidly connecting said xed servo orice and said second passage means downstream from said restriction, and a second movable servo valve jointly ope-rative with said ixed servo orifice to control fluid pressure in said second passage downstream of said restriction, said second movable servo valve being connected and positioned by said governor ilyweight and spring means.

5. In `a governor as claimed in claim 4 including' an adjustable restriction in said second lpassage means downstream of the connection between said second and third passage means -to control the rate of movement of said piston member.

6. In a governor as claimed in claim 4 including an adjustable restriction in said second passage means upream of the connection between said second and third passage means, said adju-stable restriction adapted to be `adjusted to a full off or no ow position to thereby inactivate said piston member.

7. In `a governor as claimed in claim 4 wherein the connection between said iiyweight and spring means and said lirst and second movable servo valves is a pivoted lever, said tlyweight acting on one side of said lever tending to rotate said lever in a first direction, said spring means acting on another side of said lever tending to rotate said lever in a second direction, and an adjustable roller lmember interposed between said spr-ing means and said lever to adjust the moment arm of the force produced by said spring means and thereby vary the effectiveness thereof.

8. In a governor, the combination of rst and second movable control valve members, speed error responsive means operative to cont-rol the position of said first and second movable control valves, a movable servo orifice operative with said first movable control valve to dene a first effective area, means responsive to said rst effeetive area to control the rate of fuel delivery in response thereto, a fixed servo orice member operative with said second movable control valve to define a second eiective area, a piston member responsive to said second eiect-ive area, said piston member connected to said movable ori'lice member to control the position thereof.

9. ln a governor as claimed in claim 8 wherein said fixed oritce member and said second movable control valve having a null value of said second effective area, said piston member movable in direction and at a rate corresponding to direction and degree of departure of said second effective area from said null value.

l0. In a governor, the combination of hydraulic servo means including a movable servo valve member and a movable servo orifice member jointly operative to produce an output control signal that varies in proportion to the relative distance between said servo valve member and servo orifice member, speed means for generating an error signal responsive to the difference between actual and selected speed, irst control mean-s responsive to the error generated by said speed means for controlling the degree of movement of one of said movable servo mem bers in proportion to said error, and second cont-rol means responsive to the error generated by said speed means for controlling the rate of movement of the other of said movable servo members.

References Cited in the tile of this patent UNITED STATES PATENTS 

